In a tubeless pneumatic tire, the inner surface of the tire is lined integrally with an air permeation prevention layer (an inner liner), and a butyl rubber excellent in air non-permeability is used as a material for the air permeation prevention layer. However, although there is an increasing demand for a reduction in weight of pneumatic tires, it has been difficult to achieve the reduction in weight when using the butyl rubber because the butyl rubber has a large specific gravity. In this respect, Patent Document 1 proposes the use of a thermoplastic resin film having a small specific gravity as an air permeation prevention layer instead of such butyl rubber so as to enable the reduction in weight of a pneumatic tire.
However, the thermoplastic resin film has no such air absorbability as the butyl rubber has. For this reason, a problem arises in that, if air is trapped in an uncured tire in the forming of the uncured tire, the trapped air leads to occurrence of blisters in an inner surface of the thermoplastic resin film after a curing process.
A green tire before a curing process is formed as follows. A cylindrical thermoplastic resin film 6 is first wrapped around a making drum 20 as shown in Part 5A of FIG. 5. Subsequently, an unvulcanized tie-rubber sheet 7 is wound on the thermoplastic resin film 6 by one round as shown in Part 5B of FIG. 5. Thereafter, both end portions 7a and 7b of the unvulcanized tie-rubber sheet 7 are overlapped and spliced with each other to form a step-like spliced portion 11. A void 10 of trapped air having a triangular cross-sectional shape is formed between the step-like spliced portion 11 and the thermoplastic resin film 6 as shown in FIG. 6. In this state, a carcass layer is stacked thereon, so that a green tire is formed. If the green tire thus formed is cured, the air in the void 10 is not fully absorbed into the rubber layer, thus leading to occurrence of blisters. Such blisters not only significantly disfigure the inner surface of the tire, but also may cause a breakage or separation of the thermoplastic resin film during use of the tire.
Particularly, consider a case of tires, such as heavy-duty tires, in which a carcass lifting caused during a curing process is so large that an inner liner is likely to bite into carcass cords constituting a carcass layer. In this case, because a tie-rubber sheet needs to be formed with a large thickness in order to prevent the biting, such tires have a problem in that the aforementioned failure is more likely to occur.
Patent Document 1: Japanese patent application Kokai publication No. Hei 8-258506